The present invention relates to systems, and elements, components, and compositions therefor, comprising substituted diacetylenic monomer components which are useful in monitoring and indicating the elapse of a predetermined integral of deleterious ambient conditions, such as time, temperature, humidity, actinic radiation, vaporous atmosphere, and the like, to which an associated product has been exposed and which thereby establish the shelf life of such a product. In particular, the invention provides means for economically preparing such monomer components as highly active, reduced-size particles which exhibit remarkable consistency over a narrow range of size distribution.
Typically, in monitoring the useful shelf life, i.e., the span of safe or potent utility, of a product of foodstuff, medicament, or the like which is known to be affected by, for example, a thermal ambient, an indicator system, often in the form of an affixed label, is associated with the product and exhibits a readily discernible property variation, such as a change of color or color density, at the end of the product's shelf life. To this end, such a system may comprise a thermally reactive composition appropriately formulated to provide such a color change response substantially concurrently with elapse of a given time-temperature integral commensurate with expiration of the product's predesignated shelf life. Of particular utility in such responsive compositions of shelf life monitoring systems are substituted diacetylenic monomer components which exhibit a distinct color change as a result of and generally concomitant with a solid state polymerization effected by changes in ambient conditions; for example, as in the case of a time-temperature indicator (TTI) system, an integral of time and temperature.
The distinct responses, e.g., color changes, of diacetylenic monomer components to thermal and other environmental stimuli provide bases for numerous highly functional and reliable monitoring system embodiments. One widely utilized type of such a system is implemented by incorporating a selected reactive monomer component into a composition formulated as a printable ink which is applied to a label capable of being associated, by adhesive layer or other means, with a target shelf life-limited product, such as an item of foodstuff or medicament. Selected to react in solid state polymerization to variant temperature ambients over a time period satisfying an integral matching the shelf life of the associated product, the diacetylenic component of an applied TTI label ink composition displays a predesignated color or color density signaling expiration of that shelf life.
Substituted diacetylenic monomers have been studied and utilized in shelf life monitoring systems for a substantial time. For instance, such utility of these numerous active monomers comprising at least two conjugated acetylene groups (—C≡C—C≡C—) and their unique physico-chemical properties, e.g., responsiveness to persistent temperature excursions by transforming into contrastingly colored solid state polymerization reaction products, have been described by Patel et al. (U.S. Pat. No. 3,999,946). The synthesis of these monomers and their incorporation into TTI and other shelf life indicator compositions are discussed there at length and continue to be useful in implementing embodiments of such systems. Also, the use of these diacetylenic monomer shelf life system components and improvements thereon, including broad ranges of substituents and complexes, and improved methods of monomer synthesis and blending in co-crystallization operations, have been described further by Patel (U.S. Pat. Nos. 4,189,399 and 4,384,980) and Preziosi et al. (U.S. Pat. Nos. 4,789,637 and 4,788,151). Such useful descriptions and examples of these diacetylenic monomer components finding application in shelf life monitoring systems to which the present invention relates are incorporated herein by reference. It should be noted that although the term “monomer” is used consistently throughout this specification with respect to the active monitor component materials, dimeric and polymeric component compounds of similar basic structure, as previously described in the cited references, are likewise to be considered included in this description.
As noted in the referenced specifications, numerous diacetylenic monomers may be synthesized to yield TTI components of widely varying reactive temperature ranges and resultant color densities. While such monomer components may generally be relied upon to exhibit reproducible results as indicators of shelf life end points, physical and morphological variables in these components, for example the size of their crystalline particles, often have a profound effect upon their response and performance in TTI and other monitoring applications. In addition, further requirements of crystal size limitation are often imposed by the ultimate utilization of the diacetylenic monomer composition, as in the need for sufficiently fine particles to enable formulation of a free-flowing printing ink.
Means for achieving such proper morphology, e.g., sufficiently small and uniform particle size, for diacetylenic monomer components of shelf life monitoring systems have heretofore been reliant, as described in the referenced art, upon expensive, low-efficiency intermediate operations for grinding or pulverizing these active materials. However, operations of this type not only are uneconomical, but they consistently degrade the monomer materials due to the unavoidable generation of heat, along with uncontrolled size reduction over the entire mass of monomer particles with a resultant excessive range of particle sizes.
There has thus existed for some time a need for a ready, reliable, and cost-effective means for achieving and controlling variation in reduced particle size active diacetylenic monomer components for use in TTI and other exposure integral monitoring systems without severely interrupting the system composition process by imposition of costly and inefficient grinding operations. The present invention obviates the noted shortcomings and disadvantages in the preparation of prior diacetylenic monomer component system products and provides means for readily and economically obtaining such monomer components within narrow ranges of desirably small particle sizes which have been shown to provide exceptionally consistent responsiveness in TTI and other such systems. The invention provides such diacetylenic monomer component products which comprise improved and highly effective shelf life systems while greatly reducing costs and achieving significant savings in time and material resources during system formulation.